1. Field of the Invention
The present invention relates to a discharged-sheet stacking device of an image forming apparatus, and more particularly, to a discharged-sheet stacking evice of an image forming apparatus using ink.
2. Description of the Related Art
Ink-jet printers perform printing by discharging an ink liquid onto a recording sheet. Hence, if the printed surface of the sheet touches another object before the discharged ink liquid is fixed by drying, the printed surface will be stained. In order to solve such a problem, some ink-jet printers incorporate a heater for rapidly drying the ink. Other ink-jet printers include a discharged-sheet stacking device for preventing, while executing continuous printing, a sheet from being superposed on and staining a previously printed sheet on which the ink is not yet dried.
FIG. 6 is a perspective view of a conventional ink-jet printer including a discharged-sheet stacking device. FIG. 7 is a perspective view of the discharged-sheet stacking device of the ink-jet printer of FIG. 5.
A sheet P is conveyed by an internal sheet conveying mechanism (not shown) after a printing operation, and is discharged from a sheet discharging port 2. Openable/closable movable supporting members 30 for temporarily holding sheets after printing are provided in front and at both sides of sheet discharging port 2. The supporting members 30 are operated by a cam mechanism (not shown) or the like. A discharged-sheet tray 34 where sheets after printing are finally mounted is provided under the supporting members 30.
The sheet P, after printing, is first discharged along the supporting members 30. The sheet P is held by the supporting members 30 for a predetermined drying time period. Accordingly, the sheet P is not placed on top of the immediately previously printed sheet P1 or allowed to rub against it. The drying time period is the time required for ink on the sheet P1 mounted on the discharged-sheet tray 34 to dry.
After the lapse of the drying time period, the interval between the supporting members 30 is made wider than the width of the sheet by operating the cam mechanism, and the sheet P drops onto the sheet P1.
In an ink-jet printer including such a stacking device, the time period until sheets are placed on top of one another can be secured while printing is performed on each sheet. Accordingly, it is possible to provide ink with a time period for drying, and to prevent sheets from being stained due to superposition and rubbing.
In recent ink-jet printers, however, printing speeds have increased, so that a time period which can be utilized for drying ink is reduced. Furthermore, since various types of recording materials are being developed, some recording materials require a longer time period for drying ink than ordinary recording materials. Hence, in conventional discharged-sheet stacking devices, there is the possibility that a sufficient drying time period cannot be secured, thereby producing ink stains due to superposition and rubbing of sheets. In order to overcome such problems, it is necessary to dry ink by providing a waiting time period during printing or sheet discharging. Hence, an ink drying process is an obstacle for an increase in the printing speed of ink-jet printers.